<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = 2;
        function f() {
            var b = a;
            return function () {
                b++
                return b;
            }
        }
        var fn = f()
        console.log(f()());
        console.log(f()());
        console.log(fn())
        console.log(fn())
    </script>
</body>

</html>